*: replace binary-tree library from petar/GoLLRB to google/btree.

[winkyao]

the petar/GoLLRB is not active many years, some cases, TiDB will panic in llrb.flip().

@coocood @shenli @tiancaiamao PTAL

I use below benchmark cases:

package testllrb

import (
	"flag"
	"math/rand"
	"testing"

	// "github.com/petar/GoLLRB/llrb"
	llrb "github.com/google/btree"
)

var btreeDegree = flag.Int("degree", 32, "B-Tree degree")

// Int implements the Item interface for integers.
type Int int

// Less returns true if int(a) < int(b).
func (a Int) Less(b llrb.Item) bool {
	return a < b.(Int)
}

// perm returns a random permutation of n Int items in the range [0, n).
func perm(n int) (out []llrb.Item) {
	for _, v := range rand.Perm(n) {
		out = append(out, Int(v))
	}
	return
}

const benchmarkTreeSize = 100000

func BenchmarkInsert(b *testing.B) {
	b.StopTimer()
	insertP := perm(benchmarkTreeSize)
	b.StartTimer()
	i := 0
	for i < b.N {
		tr := llrb.New(*btreeDegree)
		for _, item := range insertP {
			tr.ReplaceOrInsert(item)
			i++
			if i >= b.N {
				return
			}
		}
	}
}

func BenchmarkDelete(b *testing.B) {
	b.StopTimer()
	insertP := perm(benchmarkTreeSize)
	removeP := perm(benchmarkTreeSize)
	b.StartTimer()
	i := 0
	for i < b.N {
		b.StopTimer()
		tr := llrb.New(*btreeDegree)
		for _, v := range insertP {
			tr.ReplaceOrInsert(v)
		}
		b.StartTimer()
		for _, item := range removeP {
			tr.Delete(item)
			i++
			if i >= b.N {
				return
			}
		}
		if tr.Len() > 0 {
			panic(tr.Len())
		}
	}
}

func BenchmarkGet(b *testing.B) {
	b.StopTimer()
	insertP := perm(benchmarkTreeSize)
	removeP := perm(benchmarkTreeSize)
	b.StartTimer()
	i := 0
	for i < b.N {
		b.StopTimer()
		tr := llrb.New(*btreeDegree)
		for _, v := range insertP {
			tr.ReplaceOrInsert(v)
		}
		b.StartTimer()
		for _, item := range removeP {
			tr.Get(item)
			i++
			if i >= b.N {
				return
			}
		}
	}
}

the petar/GoLLRB got:

❯ go test -bench=.
goos: darwin
goarch: amd64
pkg: gowink.cn/test
BenchmarkInsert-8   	 2000000	       738 ns/op
BenchmarkDelete-8   	 1000000	      1114 ns/op
BenchmarkGet-8      	 3000000	       497 ns/op
PASS
ok  	gowink.cn/test	10.146s

and google/bree got:

❯ go test --degree 32 -bench=.
goos: darwin
goarch: amd64
pkg: gowink.cn/test
BenchmarkInsert-8   	 3000000	       471 ns/op
BenchmarkDelete-8   	 3000000	       526 ns/op
BenchmarkGet-8      	 3000000	       475 ns/op
PASS
ok  	gowink.cn/test	10.829s

❯ go test --degree 2 -bench=.
goos: darwin
goarch: amd64
pkg: gowink.cn/test
BenchmarkInsert-8   	 1000000	      1309 ns/op
BenchmarkDelete-8   	 1000000	      1316 ns/op
BenchmarkGet-8      	 2000000	       997 ns/op
PASS
ok  	gowink.cn/test	12.086s

when google/btree's degree set to 32, is more effective.

ref https://opensource.googleblog.com/2013/01/c-containers-that-save-memory-and-time.html

[coocood]

@winkyao
We should remove github.com/petar/GoLLRB in glide.yml.

[coocood]

@winkyao
Well, btree depends on llrb.

[winkyao]

/run-all-tests

[tiancaiamao]

/run-all-tests

[shenli]

Any benchmark result?

[coocood]

LGTM

[winkyao]

@shenli on my first comment

[tiancaiamao]

LGTM